The present invention relates to a position indicating plastic control valve for handling the flow of fluids. More particularly, the plastic valve has a poppet position indicator that moves significantly more than the valve poppet and has axial movement stops which overcome the valve's mechanical advantage and axial force thereby giving the valve high integrity and a long useful life.
Highly corrosive fluids, such as acids, are used in many industries, as in the processing of semi-conductor wafers. The corrosive effects of such fluids or liquids is further increased when their application requires that the liquids be heated to temperatures ranging from 20.degree. to 150.degree. C. which will increase the corrosive effects of the fluids.
The handling and control of heated corrosive fluids in measured amounts has been problematic. Known valves having metallic parts are short lived in that their exposure to corrosive fluids will eventually destroy the valve. Furthermore, many applications absolutely require that metallic particles not be permitted to enter into the stream of the corrosive fluids or liquids which may destroy the usefulness of such fluids.
Construction of valves out of polymers or plastics resistant to heated corrosive fluids is known. Some plastic valves have a handle for rotational adjustment which translates into axial movement of the valve poppet toward the valve seat. Substantial mechanical advantage accompanies this translated force which will eventually wear out and tear down the valve poppet and seat as well as other internal parts with repeated opening and closing of the plastic valve.
Valve position indicators are known which allow the user to known where the valve is positioned, whether it is opened, closed or part way open. Such indicators simply show the poppet motion or only move the actual distance of the poppet. These indicators do not give easy visibility of the position of the valve.
There is a need for a plastic control valve that has a long life and high integrity. Movement stops within the valve should be provided as to limit the substantial mechanical advantage created by handle rotation translated into axial force and movement of the valve poppet upon the valve seat. There is also a need for a valve of whatever material that has a position indicator with movement of a magnitude greater than actual valve poppet movement thereby giving easy visibility of the position of the valve.